Torque assist for logging-while-drilling tool

ABSTRACT

A logging-while-drilling system which is positioned within the drill string of a well drilling apparatus. The system includes a tool which has a turbinelike, signal-generating valve which rotates to generate a pressure wave signal in the drilling fluid which is representative of a measured downhole condition. A mud conditioning means comprising a jet and a spinner is positioned in the drill string above the valve of said tool wherein said means imparts angular motion to at least a portion of the drilling fluid in such a manner that the power hydraulically developed by the valve as the mud flows therethrough will be a desired function of the flowrate and/or density of said mud.

United States Patent Patton 1 Feb. 18, 1975 1 TORQUE ASSIST FOR 3,705,603 12/1972 Hawk 175/50 LOGGING WHILE DRILLING TOOL 3,739,331 6/1973 Godbry et al. 340/18 LD Inventor: Bobbie Joe Patton, Dallas, Tex.

Mobil Oil Corporation, New York, NY.

Filed: Apr. 16, 1973 Appl. No.: 351,705

Assignee:

References Cited UNITED STATES PATENTS 10/1913 Moss 415/185 4/1914 DeLaval 3/1931 Wilson 11/1955 Otis et al......

3/1967 Godbry 340/18 LD Primary Examiner-Malcolm F. Hubler Assistant Examiner-N. Moskowitz Attorney, Agent, or Firm-C. A. Huggett; Drude Faulconer [57] ABSTRACT A logging-while-drilling system which is positioned within the drill string of a well drilling apparatus. The system includes a tool which has a turbinelike, signalgenerating valve which rotates to generate a pressure wave signal in the drilling fluid which is representative of a measured downhole condition. A mud conditioning means comprising a jet and a spinner is positioned in the drill string above the valve of said tool wherein said means imparts angular motion to at least a portion of the drilling fluid in such a manner that the power hydraulically developed by the valve as the mud flows therethrough will be a desired function of the flowrate and/or density of said mud.

5 Claims, 3 Drawing; Figures GENERATOR PATENIEBFEBI 81975 RECORDER PUMP ELECTRONIC SURGER PACKAGE 5 l FIG! TORQUE ASSIST FOR LOGGING-WHILE-DRILLING TOOL BACKGROUND OF THE INVENTION The present invention relates to a logging-while drilling apparatus and more particularly relates to a downhole, logging-while-drilling apparatus which includes a means for conditioning the circulating drilling fluid in such a manner that the signal-generating valve of the apparatus will develop a hydraulic torque which is a desired function of the flowrate and density of said fluid.

The desirability of a system which is able to measure downhole drilling parameters and/or formation characteristics and transmit them to the surface while actual drilling of an earth well is being carried out has long been recognized. Several such systems have been proposed and are commonly referred to as logging-whiledrilling systems. In logging-while-drilling systems, one of the major problems exists in finding a means for telemetering the information from a downhole location to the surface and having it arrive in a meaningful condition.

In this regard, it has been proposed to telemeter the desired information by means of a pressure wave signal generated in and transmitted through the circulating mud system normally associated with rotary drilling operations. The pressure wave signal which is representative of a downhole condition is generated in the mud downhole near the bit by a signal-generating valve and the wave travels up the hole through the mud to a signal processor at the surface. Logging-while-drilling systems utilizing this technique of telemetery are disclosed and fully described in US. Pat. No. 3,309,656 to John K. Godbey, issued Mar. 14, 1967, and in copending US. application Ser. No. 213,061, filed Dec. 28, 1971.

In logging-while-drilling systems of the types mentioned above, a tool having a turbinelike, signalgenerating valve is positioned in the circulating mud path near the drill bit. A motor in the tool is energized in response to a measured piece of downhole information to drive the valve at a rotational speed necessary to produce a signal in the mud which is representative of said measured information.

In the operation of tools of this type, forces are pres ent which normally oppose the rotation of the signalgenerating valve. Such forces may arise from the gradual or partial plugging or jamming of the valve by solid materials normally found in the mud or from frictional losses in the tool due to the rotation of the motor, the associated drive train, and the shaft carrying the rotor of the valve. Power to compensate for these opposing forces must come from the motor, itself, and/or hydraulic power developed by the turbinelike, signalgenerating valve as mud flows therethrough during operation. It is desirable in most instances to utilize the turbine features of the signal valve to supply at least a portion of the needed power to compensate for said opposing forces, thereby leaving the maximum power possible in the motor to accelerate, decelerate, or otherwise drive the rotor of the valve.

As is well known, the power developed by a turbine, e.g., signal-generating valve, is dependent not only on its own blade design, but also on the flowrate and density of the operating fluid. In some instances, e.g.,

where plugging or jamming of the valve is a recurring problem, it may be desirable to be able to substantially increase the force hydraulically developed by the valve (over that normally expected) by merely increasing the flowrate and density of the mud. However, in most instances, it is more desirable to maintain the force hydraulically developed by the valve at a substantially constant value which is relatively independent of the flowrate and/or density of the mud.

In early embodiments of tools of the above type where balancing internal friction losses was of primary concern, the turbine features of the valve were designed so that the valve developed zero power or torque when a particular flowrate of a fluid having a particular density was flowed through the valve. Al though this arrangement required very little increase in power from the motor to change the speed of the valve rotor to thereby generate desired signals, continuous motor power had to be used to overcome the frictional losses of the tool. This drain of motor power decreased the reserve power of the motor which might otherwise be needed in emergencies, e.g., to overcome plugging or jamming of the valve.

It was next considered that the turbine features of the valve should be so designed that the valve itself would develop a force or torque equal to but opposite in sign to frictional losses within the tool so that no excess power would be required from the motor to compensate for said frictional losses. However, it was realized that since the turbine features (i.e., pitch of the openings through the rotor) are not adjustable while the tool is downhole, this neutral power situation of the tool would only exist at the particular flowrate and density parameters used in the initial design. Since it is not uncommon for both the flowrate and/or density of the drilling mud to vary substantially during a drilling oper-. ation, the disadvantages of this approach appeared to exceed the advantages. The disadvantages arise from the fact that the positive or negative power developed by the valve increases as the flowrate or density increases or decreases, respectively, so that the additional power from the motor to overcome the hydraulically generated power of the valve at a changed mud condition far exceeds the frictional losses being cancelled by said power at said designed rate. Accordingly, in those instances where the power developed by the valve is to be used to nullify the substantially constant frictional losses in the tool, this power should be of a relatively constant value and one which is substantially independent of both flowrate and density of the circulating fluid.

SUMMARY OF THE INVENTION The present invention provides a logging-whiledrilling system of the type described above which includes a mud conditioning means positioned in the circulating mud stream above the signal-generating valve of a logging-while-drilling tool wherein said means normally imparts angular motion to at least a portion of the mud in such a manner that the power developed as the mud flows through said valve will be a desired function of the flowrate and/or density of said mud.

More particularly, the mud conditioning means is comprised of a unit having two principal elements, a jet and a mud spinner. The jet is one having both a smooth entrance and a smooth exit to avoid creating unwanted turbulence in the mud stream as it flows therethrough. The mud spinner is preferably comprised of a plurality of vanes having a desired pitch, said vanes being fixed against rotation immediately below the jet.

The jet produces a mud flowrate and densitydependent, radial mud velocity profile in the vicinity of the spinner. As the mud momentum (dependent on flowrate and density) increases, the force of the mud exiting the jet increases, thus increasingthe velocity of the mud nearer the center of the spinner causing a larger fraction of the mud to flow through the central portion of the spinner where little or no spin is imparted to the mud. A reduced fraction of the mud flows through the larger or outer radii of the spinner where angular motion is imparted to said reduced mud fraction. By coordinating the jet and the spinner through the use of an adjustable diverter tube positioned within the central portion of the spinner, the total mud stream will be given desired angular or rotational properties before said mud passes through the signal-generating valve. By knowing these angular or rotational properties, the turbine features of the valve can be designed so that the valve will develop a predetermined force or torque as the mud passes therethrough. The mud conditioning means may be designed to increase or decrease the angular or rotational properties of the mud delivered to the valve as a function of flowrate and/or density or, as in the preferred embodiment, the conditioning means may be designed to impart substantially constant angular or rotational properties to the mud which are relatively independent of the flowrate and/or density of the mud throughout expected operating ranges.

BRIEF DESCRIPTION OF THE DRAWINGS The actual construction, operation, and the apparent advantages of the invention will be better understood by referring to the drawings in which like numerals identify like parts and in which:

FIG. 1 is a schematic elevation of a rotary drilling apparatus including in vertical section a well containing a drill string in which the present invention is employed;

FIG. 2 is a schematic elevation, partly in section, of a portion of the drill string of FIG. 1, having the present invention mounted therein; and

FIG. 3 is a detailed perspective view of the mud spinner of the present invention.

I DESCRIPTION OF THE PREFERRED EMBODIMENT Referring more particularly to the drawings, FIG. 1 discloses the present invention as used in a loggingwhile-drilling system which is incorporated in a rotary drilling apparatus. A derrick 21 is disposed over a well 22 being formed in the earth 23 by rotary drilling. A drill string 24 is suspended within the well and has a drill bit 27 at its lower end and a kelly 28 at its upper end. A rotary table 29 cooperates with kelly 28 to rotate string 24 and bit 27. A swivel 33 is attached to the upper end of kelly 28 which in turn is supported by hook 32 from a traveling block (riot shown). This arrangement not only supports the drill string 24 in an operable position within well 22, but also forms a rotary connection between the source of circulating drilling fluid, such as mud, and the dril string 24. It should be understood that mud" as used throughout this disclosure is intended to cover those fluids normally used in rotary drilling operations.

The pump 36 transfers drilling mud from a source, such as pit 34, through desurger 37 into mudline 38. Desurger 37 is adapted to reduce the pulsating effect of pump 36 as is well known in the art. The mud flows through mudline 38, flexible hose 39, swivel 33, drill string 24, and exits through openings (not shown) in drill bit 27 to pass outward into well 22. The mud then circulates upward carrying drill cuttings with it through the annulus between the well and drill string 24 to the surface of the earth 23. At the surface, well head 41 is secured to casing 40 which is cemented in the well 22. Pipe 42 is connected to casing 40 for returning the mud to pit 34.

As schematically illustrated in FIGS. 1 and 2, a logging-while-drilling tool 46 is located in drill collar 26 which forms a part of the lower end of drill string 24 near bit 27. Tool 46 has a motor-actuated, turbinelike, signal-generating valve which periodically interrupts at least a portion of the drilling fluid flowing through the valve to thereby generate a pressure wave in the fluid having characteristics which are representative of some piece of measured downhole information. This is the same basic type of logging-while-drilling tool which is disclosed and described in US. Pat. No. 3,309,656. Although the present invention is primarily directed to a means for conditioning the mud ahead of the signal generating valve so that said valve will develop a defined hydraulic torque when rotated by the mud passing therethrough, a brief description of the entire tool 46 is considered helpful in fully understanding and appreciating the present invention.

A transducer means which is capable of measuring a desired downhole condition and converting the measurement to an electrical signal is positioned downhole on or near tool 46. As illustrated, transducer means 54, e.g., a strain gauge, is positioned on drill collar 26 to measure the downhole weight on bit 27. The signal from transducer means 54 is applied to electronic package 53 which is sealed in compartment 48 of tool housing 46a. For examples of package 53, see US. Pat. No. 3,309,656, or preferably US. application Ser. No. 213,061, filed Dec. 28, 1971. Power from electric power generator 50 in compartment 49 of housing 46a is used to drive the variable speed, electric motor in compartment 47 of housing 46a. A turbine 52 driven by the mud flow rotates generator 50 to produce electrical power. Motor 55 is controlled by circuitry in package 53 to drive rotor 61 of signal-generating valve through drive train 56 to thereby generate a pressure wave signal in the mud which is representative of the information to be transmitted.

In the present invention a means is provided which conditions the mud before it reaches valve 60 of tool 46 in such a way that the angular or rotational properties applied by the mud to valve 60 will be a desired function of the flowrate or density of the mud. Mud conditioning means 70 is comprised of two principal elements, jet 7! and mud spinner 72. Jet 71 is affixed in drill collar 26 and has a smooth, tapered throat entrance 71a and a smooth, curved exit 71b to prevent unwanted turbulence of the mud as it passes through jet Spinner 72 is preferably comprised of a plurality of vane members 73 which are affixed in drill collar 26 immediately below jet 71. Vane member 73, as illustrated, terminates at a distnace x from the centerline of collar 26, thereby forming an open central portion 74 of spinner 72. Each of vane members 73 has a degree of pitch or cant necessary to impart a desired spinning action to the mud as will be more fully described below.

During a drilling operation, mud is circulated by pump 36 down drill string 24 where it must pass through jet 71. The mud passing through jet 71 produces a mud flowrate and density-dependent radial mud velocity profile in the vicinity of spinner 72. As the mud momentum is increased (this momentum being a function of flowrate and density of the mud), the force of the mud exiting the jet is increased, thus increasing the velocity of the mud stream near the central portion 74 of spinner 72. That is, a larger fraction of the entire mud stream will flow through central portion of spinner 72 where little or no spin is given to the mud. A reduced fraction of the mud stream flows through the outer portion of spinner 72 where it is spun, thereby imparting desired angular or rotational motion thereto. Likewise, if flowrate or density of the mud is decreased, a lesser fraction of the mud stream will flow through the central portion 74 and a greater fraction will flow through the outer portion with the net results being that a greater fraction of the mud stream will have angular or rotational motion imparted thereto.

To better regulate the actual amount of the flow stream which will be spun, center diverter tube 75 is adjustably positioned within central portion 74 of spinner 72. Tube 75 is a substantial barrier to further divergence of the radial velocity profile after the mud enters the tube. A further advantage of tube 75 is that the lengths of vane members 73 below the upper end of tube 75 have little or no effect on the fractional division of the mud. As will be explained below, positioning of tube 75 with respect to the exit of jet 71 regulates the fraction of the mud stream that will be given angular motion and accordingly determines the desired relationship between the flowrate and density of the mud and the resultant force to be delivered to the valve by the mud.

in a typical application of mud conditioning means 70, jet 71 and spinner 72 are installed into a flow conduit such as drill collar 26. Vane members 73 are purposely canted at an angle which, in the absence of tube 75, would produce throughout the flowrate and density ranges to be encountered during a drilling operation an excess of angular or rotational properties to the mud stream over that necessary for valve 60 to produce a desired force as the mud passes therethrough. Tube 75 is then inserted into central portion 74 of spinner 72 and moved to various vertical positions therein. Rotational properties of the mud are measured at the various positions until the desired position of tube 75 is determined. Tube 75 is then affixed to spinner 72 at this position by spot welding or the like, and conditioning means 70 is ready for use.

It is noted that each position of tube 75 within central portion 74 will produce a different value of angular or rotational properties of the mud which is a function of the flowrate and/or density of the mud stream. That is, when tube 75 is in the lower part of portion 74, the resultant angular or rotational properties of the mud exiting spinner 72 will increase as the mud flowrate and/or density is increased. The rate of increase of these properties per unit of increase of flowrate and/or density, however, will decrease as tube 75 is moved upward until a null point is reached within central portion 74 wherein the rate of increase is zero. At this null point,

the angular or rotational properties of the mud will re main substantially constant even when a change occurs in flowrate and/or density of the mud stream. Continued upward positioning of tube beyond this null point results in a decrease of rotational properties of the mud whenever the mud flowrate and/or density is increased.

In the preferred mode of operation of the present invention, tool 46 develops significant internal power losses due to the friction created by the rotation of motor 55, gear train 56, and rotor shaft 61a. To drive or maintain rotor 61 at a desired rotational speed or to vary the speed when necessary, these frictional losses must be compensated for by supplying additional power from motor 55 and/or by hydraulically developing torque from the turbinelike features of valve 60. Since the power of motor 55 is limited due to the relatively small space available, it is desirable to use the torque developed by the mud passing through valve 60 to offset the internal frictional losses of tool 46, thereby leaving as much reserve power as possible in motor 55 for other contingencies.

It is possible to merely design valve 60 so that the openings 6112 through rotor 61 have a desired pitch which will allow valve 60 to develop the desired torque when a defined flowrate of a circulating fluid having a defined density flows therethroughl However, it can be seen from the above discussion that if the flowrate and- /or density of the circulating fluid varies, the torque developed by valve 60 will also vary. Since this change in torque is a function of the flowrate and density and since changes in both flowrate and. density are common in typical drilling operations, the excess power required from motor 55 to counteract these torques at changed flowrates or densities is normally substantially greater than the power required to balance the frictional losses within tool 46. Therefore, in designing valve 60 to develop a constant torque, it is necessary that this torque be substantially independent throughout the muds normal operating ranges of flowrate and/or density.

As explained above, tube 75 can be positioned within central portion 74 of spinner 72 so that the angular or rotational properties of the mud will remain substantially constant with any change of flowrate and/or density of the mud stream.

By use of mud conditioning means 71 with tube 75 properly positioned, the mud stream arriving at valve 60 of tool 46 will have constant angular or rotational properties which are substantially independent of the flowrate and the density of the mud. By designing the turbine features of valve 60 based on these constant properties, the torque developed by said valve will remain substantially constant even when the flowrate and/or the density of the mud is changed.

Although it should be recognized that the actual design features of mud conditioning means 71 will depend on the operating environment in which it is to be used, the following example including generalized design criteria is considered illustrative of the present invention.

The throat area of jet 71 must be substantially less than the cross-section area in the vicinity of spinner 72, Le, the internal cross-sectional area of collar 26. A good design factor in this regard is to make the jet throat area approximately one-fourth that of the area in the vicinity of spinner 72. Further, the diameter of diverter tube 75 should be about the same as the diameter of the throat of jet 71 which in turn should be approximately one-half the outside diameter of spinner 72. The distance from the throat of jet 71 to the top of diverter tube 75 is adjustable as explained above. The length of vanes 73 is not critical and a length of four jet throat diameters is normally adequate in most instances. The pitch of vanes 73 is a function of other design factors, i.e, fraction of mud spun, hydraulic power wanted, speed of valve 60, and the pitch of the vanes of valve 60. For example, where valve 60 has vertical vanes and runs at 160 rpm with zero hydraulic torque being desired from a mud flowrate of 400 gallons per minute of which one-half is to be spun by spinner 72, the pitch of vanes 73 would be about 8.

fluid comprising:

a jet positioned in said conduit so that said drilling fluid will pass therethrough; and

a means positioned in said conduit below said jet for imparting angular motion to at least a portion of said drilling fluid after it exits said jet and before it passes through said valve means.

2. The apparatus of claim 1 wherein said means-for imparting angular motion to at least a portion of said' drilling fluid comprises:

a plurality of vane members.

3. The apparatus of claim 2 wherein each of said vane members is fixed in said conduit against rotation and wherein each of said vane'mem'be'rs terminates at a distance from the centerline of said conduit to thereby de fine an open, central portion through said vane members.

4. The apparatus of claim 3 including:

a diverter tube positioned within said central portion of said vane members.

5. The apparatus of claim 1 wherein said jet has a smooth entrance and a smooth exit to prevent turbulence of said drilling fluid as it passes through said jet. l 

1. A logging-while-drilling apparatus for use in an earth drilling operation comprising: a conduit adapted to be connected into a drill string of an earth drilling apparatus; a logging-while-drilling tool positioned within said conduit, said tool having a turbinelike, signal generating valve positioned so that at least a portion of any drilling fluid flowing through said conduit will flow through said valve; and means in said conduit upstream of said valve for conditioning said drilling fluid comprising: a jet positioned in said conduit so that said drilling fluid will pass therethrough; and a means positioned in said conduit below said jet for imparting angular motion to at least a portion of said drilling fluid after it exits said jet and before it passes through said valve means.
 2. The apparatus of claim 1 wherein said means for imparting angular motion to at least a portion of said drilling fluid comprises: a plurality of vane members.
 3. The apparatus of claim 2 wherein each of said vane members is fixed in said conduit against rotation and wherein each of said vane members terminates at a distance from the centerline of said conduit to thereby define an open, central portion through said vane members.
 4. The apparatus of claim 3 including: a diverter tube positioned within said central portion of said vane members.
 5. The apparatus of claim 1 wherein said jet has a smooth entrance and a smooth exit to prevent turbulence of said drilling fluid as it passes through said jet. 